Human milk bile salt-activated lipase (BAL) is a physiologically important enzyme in the intestinal fat digestion processes of infants. The goal of this project is to understand the structure and function relationships of this enzyme. The aspects of the proposed studies are summarized in the following. (1) We propose to determine the sequence of its cDNA. This will provide a structural framework for the functional interpretations. (2) The identification and structure determination of the active site will help define the nature and location of functional groups essential for the functional interpretations. (3) The further understanding of the enzyme kinetics will be instrumental for gaining an understanding of the catalytic mechanism of BAL. (4) The cloned human milk BAL cDNA will be expressed in mammalian cell culture which will be used to carry out site-directed mutagenesis experiments. This approach will permit the pin-point examination of the roles of functionally important residues in BAL by muta- genesis experiments. (5) The structure-function information generated for human milk BAL will also facilitate a comparative study on the pancreatic BAL. These studies may include the determination of cDNA structure and the kinetic studies of pancreatic BAl.